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Leptin, tumor necrosis factor- (TNF), and CD14 in ovine adipose tissue and changes in circulating TNF in lean and fat sheep²

J. A. Daniel^*, T. H. Elsasser, C. D. Morrison, D. H. Keisler, B. K. Whitlock, B. Steele, D. Pugh and J. L. Sartin^,1

^* South Dakota State University, Brookings, SD 57007; and United States Department of Agriculture, Beltsville, MD 20705; and University of Missouri, Columbia, MO 65211; and and Auburn University, Auburn, AL 36849

¹ Correspondence: 212 Greene Hall (phone: 334-844-5515; fax: 334-844-5388; E-mail: sartijl{at}vetmed.auburn.edu).

Four studies were designed to determine whether 1) tumor necrosis factor- (TNF) and the Lipopolysaccharide (LPS) binding ligand, CD14, are produced by sheep adipose tissue; 2) nutritional reserves and/or short-term fasting affect circulating concentrations of TNF; 3) there is a relationship between TNF and metabolic factors in sheep; and 4) inflammation alters circulating concentrations of leptin. In Exp. 1 and 2, ewes were assigned, based on ultrasonic assessments of last-rib subcutaneous fat measurements to fat (fat thickness >1 cm; mean = 1.52 ± 0.03 cm) or thin (fat thickness <1 cm; mean = 0.25 ± 0.03 cm) groups. Fat and thin ewes were assigned to fed or fasted groups for a total of four groups (fed-fat; fasted-fat; fed-thin; fasted-thin). Fed-ewes had ad libitum access to feed, and fasted-ewes were prohibited feed 48 h before initiation of sample collection. In Exp. 1, subcutaneous fat samples were collected from just above the last rib for detection of TNF and CD14 mRNA, and immunoreactivity. Tumor necrosis factor--like immunoreactivity in adipocytes was sparse, more pronounced in cells in fed-ewes than fasted-ewes, and localized to membranes between adjacent cells in nucleated regions. Immunoreactivity for CD14 was minimally observed but present in adipocytes and widely expressed in infiltrating monocytes and epithelial vascular cells. Leptin was detected in adipocytes. In Exp. 2, plasma samples collected every 6 h for 24 h were analyzed for plasma concentrations of TNF. Fat ewes had greater plasma concentrations of TNF than thin ewes (P = 0.039). In Exp. 3, wethers were injected i.v. with interleukin-1ß or TNF. Blood samples were collected every 15 min for 8 h following injection. Plasma concentration of leptin was not affected by treatment (P > 0.39). In Exp. 4, wethers were injected with LPS. Blood samples were collected every 15 min for 8 h following injection. Plasma concentration of leptin was not altered by LPS (P > 0.20). These results provide evidence: 1) of TNF-like immunoreactivity within fat tissue; 2) that elements within fatty tissues have CD14 that may allow adipocyte function to be directly affected by LPS; 3) that plasma concentrations of leptin are not altered by LPS treatment; and 4) that circulating concentrations of TNF are elevated with obesity in sheep.

Key Words: Fat • Leptin • Lipopolysaccharides • Receptors • Sheep • Tumor necrosis factor

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